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Science : Suicidal nerve cells take away the pain

By Andy Coghlan

THE cause of a rare hereditary disease which makes sufferers insensitive to
pain has been tracked down by researchers in Japan. The finding could lead to
more effective painkillers.

Yasuhiro Indo and his colleagues in the paediatrics department at the
Kumamoto University School of Medicine examined DNA from four people suffering
from CIPA, or chronic insensitivity to pain with anhidrosis (inability to
sweat). They found defects in the gene that makes tyrosine kinase-A (TRKA), a
receptor on embryonic neurons. This confirmed what pain researchers had
suspected from experiments on animals—that without the receptor, embryonic
cells die before they can mature into specialised sensory neurons for detecting
tissue damage and feeling pain.

People with CIPA can feel objects they touch, but cannot sense tissue damage.
“They could feel a pencil, for example, but not sense pain if they stubbed their
toe,” says John Wood, a specialist in pain research at University College
London. Neither can they respond to heat by sweating, because they do not have
the necessary neurons in their sweat glands.